The present invention relates to high-power electrical switches, and in particular to a flexible cable assembly for remotely actuating electrical switches such as circuit breakers.
High-power electrical circuitry is normally placed inside a metal cabinet to protect the electrical circuitry from the external environment and to shield users from potential hazards associated with the operation of the circuitry.
Often the cabinet provides a handle that serves both to lock a cabinet door and to disconnect electrical power from the interior circuitry before the door is opened. The handle may communicate through a flexible cable assembly with a switch inside the cabinet, for example, a circuit breaker, so that when the handle is moved to allow opening of the cabinet door, the circuit breaker is also opened, removing electrical power from the interior circuitry. This feature is normally subject to the mechanical override in the event that the cabinet must be operated with the door open and the circuitry live.
A flexible cable assembly provides a substantially incompressible sheath through which a flexible cable may slide. Opposite ends of the sheath are fixed, respectively, to a stationary structure of the handle and an actuator frame attached to the circuit breaker housing. One end of the flexible cable is then attached to a movable portion of the handle to communicate this motion through the flexible cable to a slider held within the actuator frame. The slider may provide a collar capturing a toggle operator of the circuit breaker to move the circuit breaker toggle between an “on” and “off” position with movement of the flexible cable by the handle.
The end of the flexible cable of the flexible cable assembly may attached to the slider by means of a pair of opposed jam nuts attached to a threaded ferrule on one end of the flexible cable. The jam nuts are tightened against either side of a hole in the flange on the slider. Likewise, the sheath of the flexible cable assembly may be attached to the actuator frame by means of a pair of opposed jam nuts also tighten on opposite sides of a hole through a flange on the actuator frame. In both cases, the jam nuts serve the dual purpose of attaching the cable or the sheaf to corresponding structure and allowing adjustment of the relative points of attachment for “tuning” the remote actuation system.
“Tuning” adjusts the separation of the points of attachment of the flexible cable and the sheath to corresponding structure of the actuator and slide so that a given range of motion of the handle is translated to positions of the toggle operator of the circuit breaker sufficient fully switch the circuit breaker between its “on” and “oft” positions.
Assembly of the jam nuts to the respective attachment points of the slider and/or attachment frame requires that one jam nut be removed so that the threaded shaft holding the jam nuts can be inserted through the hole in the flange. The removed jam nut is then reinstalled and the two jam nuts adjusted for proper positioning. This process is cumbersome and time-consuming but allows the necessary tuning.
This latter step of tightening the jam nuts can also be difficult requiring that the actuator frame be partially disassembled and that the person making the assembly work within the close confines of that framework to loosen and tighten these two nuts. Once the two jam nuts are properly positioned they must be tightened together using torque-controlled tools to ensure that the connection does not inadvertently loosen during vibration or use and to ensure that the torque is not so high as to damage the threaded barrel on the end of the sheath causing the sheath to separate from the actuator.
After moving the jam nuts, it can be difficult to determine whether the adjustment is correct because the handle may not be operated with the jam nuts loose such as would allow the sheath to move freely. Accordingly multiple trials may be required for proper adjustment.
The slider and adapter assembly may be formed of folded metal to provide the necessary mounting flanges needed for the jam nuts. These metal parts must be lubricated to prevent seizing of the sliding operation between few contact surfaces of the slider and the actuator frame. While these metal components are robust they are electrical conductors and must be used with care in the vicinity of electrical circuitry and with consideration of conduction from the actuator through the flexible cable to the handle and the cabinet.